After decades of tape-based analog video recorders being the only means whereby home users could record and conveniently store programs screened on antenna, cable or satellite TV, with the availability of fast and at the same time inexpensive video processors and high-performance video codecs such as, say, MPEG2 (1994) and MPEG4 (1998) a number of mainly hard-disk-based digital machines providing not only straight video recording but also a number of convenience features have become available in recent years.
The term personal video recorder (PVR), or sometimes digital video recorder (DVR), is frequently used for this new generation of devices. While these modern machines can of course be used like conventional VCRs for simple recording and subsequent playback of programs, they are capable of much more than that. For example, a frequently used feature of a PVR is what is referred to as time shifting, whereby the user can begin replaying a program even while it is still recording. Thanks to the high-performance hardware of a modern PVR, the picture quality achieved is superior to that of a conventional VHS or S-VHS tape machine.
Time-shifted viewing also allows the user to “pause” a program initially being viewed live, e.g. to take a telephone call, and to resume playback later, it appearing to the user that he has actually paused the live screening and continued it later. In the background, however, pressing of the “Pause” button by the user has caused the user's PVR to record the current program, and pressing the “Pause” button again results, on the one hand, in the recorded program continuing to be recorded and, on the other, allows it to played back already.
Another very popular feature of a PVR is the ability to skip lengthy sections in a recording with minimal delay. Often this is used during playback to skip blocks of commercials contained in the recorded program. A number of services have become established around this capability which facilitate locating the boundaries of the blocks of commercials, e.g. by storing the start and end of a block as points in time relative to the beginning of a program as a recording index, thereby enabling the commercials to be automatically skipped during playback.
In addition to specially adapted entertainment electronics, multimedia PCs with suitable software are also increasingly being used as PVRs (known as home theater PCs, HTPCs). Technically there is virtually no difference between a specialized PVR and a PC PVR; both have a large (disk) memory, sufficient processor power and suitable video codecs.
By means of configurable software or firmware, both platforms are able to offer the user additional functions, such as program search, thematically geared to his favorite programs. The common feature of both platform variants is that recording takes place locally on the user's premises and the quantity of recordable programs is limited by the local disk memory. It is therefore often possible to transfer recorded programs from the device's internal memory to writable media such as re(writable) CDs or DVDs. However, this involves a cost factor and, not least, the price of a PVR is also considerable. And even PVRs suffer from the problem that recording several programs simultaneously also requires a plurality of PVRs. More expensive multi-tuner machines solve this problem only to a limited extent, as there will always be fewer tuners than TV stations and, in addition, PVR hardware that is of sufficiently high performance for one channel reveals its limitations when required to record a plurality of channels simultaneously.
To be able to offer users all the advantages of a PVR without them having to invest in a PVR, the White Paper “Network PVR: Everything on Demand”, Jay Schiller, nCube Corporation, proposes a network PVR whereby storage, encoding logic and codecs are held available in the cable network by a provider. The user gets a unit with which he can select programs to be stored and can retrieve stored programs which are then transmitted to the user in real time by means of a broadband connection. Such a device can be much less powerful than a PVR or an HTPC. At the same time the user can rent virtually unlimited storage space on the PVR server, while the operator of the PVR server only needs to keep one copy of each program which is then distributed as required to those users who have stored that program in their (virtual) store.
In a development, a network PVR of this kind can be designed so as to eliminate “programming” of the network PVR by the user, instead of which the user has access to all the shows in its program list of, for example, the last 4 weeks.
The aforementioned functions of time-shifting and fast skipping of advertising content are frequently manually combined by PVR users, whereby users record a live program, start viewing said program later in time-shift mode and progressively approach the live transmission by skipping the broadcast advertising content. Both in the case of standalone PVRs and in the case of network PVRs, a user must manually estimate how much time is used within the screening of a program for advertising content in order to be able to determine the optimal starting time for the time-shifted playback of this recording. If he starts the playback too early, his program will be interrupted by commercials at any rate toward the end. If he starts too late, although he can enjoy a commercial-free program, he was obliged to wait longer than necessary.